Communication system and synchronization method

ABSTRACT

A synchronization method is suitable between a first electronic apparatus and a second electronic apparatus. The synchronization method include following steps. A first interrupt signal is generated to trigger a first timer on the first electronic apparatus. A radio frequency packet is transmitted from the first electronic apparatus to the second electronic apparatus. In response to that the radio frequency packet is received by the second electronic apparatus, a second interrupt signal is generated to trigger a second timer on the second electronic apparatus. The second timer is synchronized with the first timer or a timestamp of the first timer is estimated according to the second interrupt signal and the radio frequency packet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/889,170, filed on Feb. 5, 2018, which claims priority to U.S.Provisional Application Ser. No. 62/456,130, filed on Feb. 8, 2017 andU.S. Provisional Application Ser. No. 62/456,133, filed on Feb. 8, 2017.All of these applications are herein incorporated by reference.

BACKGROUND Field of Invention

The present application relates to a communication system. Moreparticularly, the present application relates to a synchronizationmethod between different devices in the communication system.

Description of Related Art

When two devices are communicating with each other, these two devicesneed a common time reference, such that a transmitter of these twodevices can transmit data at correct timing and a receiver of these twodevices can sample or receive data also at correct timing. If these twodevices are not synchronized with each other, some errors may occur tothe data transmitted between these two devices. For example, the datamay contain severe jitters or noises.

SUMMARY

An aspect of the disclosure is to provide a communication system, whichincludes a first electronic apparatus and a second electronic apparatus.The first electronic apparatus includes a first control circuit and afirst radio frequency transceiver. The first radio frequency transceiveris coupled with the first control circuit. The first radio frequencytransceiver is configured to generate a first interrupt signal to thefirst control circuit and transmit a radio frequency packet. The secondelectronic apparatus includes a second control circuit and a secondradio frequency transceiver. The second radio frequency transceiver iscoupled with the second control circuit. The second radio frequencytransceiver is configured to receive the radio frequency packet andgenerate a second interrupt signal to the second control circuit inresponse to that the radio frequency packet is received. The firstinterrupt signal is configured to trigger a first timer of the firstcontrol circuit. The second interrupt signal is configured to trigger asecond timer of the second control circuit. The second timer issynchronized with the first timer or a timestamp of the first timer isestimated according to the second interrupt signal and the radiofrequency packet.

Another aspect of the disclosure is to provide a synchronization method,which is suitable between a first electronic apparatus and a secondelectronic apparatus. The synchronization method include followingsteps. A first interrupt signal is generated to trigger a first timer onthe first electronic apparatus. A radio frequency packet is transmittedfrom the first electronic apparatus to the second electronic apparatus.In response to that the radio frequency packet is received by the secondelectronic apparatus, a second interrupt signal is generated to triggera second timer on the second electronic apparatus. The second timer issynchronized with the first timer or a timestamp of the first timer isestimated according to the second interrupt signal and the radiofrequency packet.

Based on aforesaid embodiments, the second timer on the secondelectronic apparatus is synchronized with the first timer on the firstelectronic apparatus. Therefore, the data transmission between the firstelectronic apparatus and the second electronic apparatus can refer tosynchronized clock signals on the first timer and the second timerrespectively. In an embodiment, an ultrasound packet is transmittedbetween the first electronic apparatus and the second electronicapparatus, such that ultrasound transmission between the firstelectronic apparatus and the second electronic apparatus can refer tothe synchronized clock signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a functional block diagram illustrating a communication systemaccording to an embodiment of the disclosure.

FIG. 2A is a flow chart illustrating a synchronization method accordingto an embodiment of the disclosure.

FIG. 2B is a flow chart illustrating further steps in one step shown in

FIG. 2A.

FIG. 3A is a time diagram illustrating a radio frequency packettransmitted between the radio frequency transceivers according to anembodiment.

FIG. 3B is a time diagram illustrating more details about a firstinterrupt signal, the radio frequency packet, a second interrupt signalduring one frame shown in FIG. 3A according to an embodiment.

FIG. 4A is a time diagram illustrating the radio frequency packet and anacknowledge packet transmitted between the radio frequency transceiversaccording to an embodiment.

FIG. 4B is a time diagram illustrating more details about the firstinterrupt signal, the radio frequency packet, the second interruptsignal and a ultrasound signal during one frame shown in FIG. 4Aaccording to an embodiment.

FIG. 5 is a functional block diagram illustrating a communication systemaccording to an embodiment of the disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. In addition, the present disclosure mayrepeat reference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

Reference is made to FIG. 1, which is a functional block diagramillustrating a communication system 100 according to an embodiment ofthe disclosure. The communication system 100 includes at least twoelectronic apparatuses. In the embodiment shown in FIG. 1, thecommunication system 100 includes a first electronic apparatus 120 and asecond electronic apparatus 140.

The first electronic apparatus 120 and the second electronic apparatus140 are able to communicate with each other. For example, data,commands, and/or control signals can be transmitted from the firstelectronic apparatus 120 to the second electronic apparatus 140 or fromthe second electronic apparatus 140 to the first electronic apparatus120.

As shown in FIG. 1, the first electronic apparatus 120 includes acontrol circuit 122, a radio frequency transceiver 124 and an ultrasoundtransceiver 126. The control circuit 122 is coupled to the radiofrequency transceiver 124 and the ultrasound transceiver 126. In anembodiment, the control circuit 122 can be implemented by amicro-controller unit (MCU), a processor, a central processing unit(CPU), an application-specific integrated circuit (ASIC) or anyequivalent controlling circuit. In an embodiment, the radio frequencytransceiver 124 can be a wireless communication transceiver (e.g., aRFID transceiver, a WiFi transceiver, a Bluetooth transceiver or a BLEtransceiver) which transmits over electromagnetic waves. In anotherembodiment, the control circuit 122 and the radio frequency transceiver124 can be implemented by one integrated circuit unit, such as a radiofrequency transceiver with a control logic component. The radiofrequency transceiver 124 is able to transmit a radio frequency packetRP to one target device (i.e., the second electronic apparatus 140 inthe embodiment). The ultrasound transceiver 126 can also be a wirelesscommunication transceiver which transmits over ultrasound waves. Theultrasound transceiver 126 is able to transmit an ultrasound packet UPto the target device.

As shown in FIG. 1, the second electronic apparatus 140 includes acontrol circuit 142, a radio frequency transceiver 144 and an ultrasoundtransceiver 146. The control circuit 142 is coupled to the radiofrequency transceiver 144 and the ultrasound transceiver 146. In anembodiment, the control circuit 142 can be implemented by amicro-controller unit (MCU), a processor, a central processing unit(CPU), an application-specific integrated circuit (ASIC) or anyequivalent controlling circuit. In an embodiment, the radio frequencytransceiver 144 can be a wireless communication transceiver (e.g., aRFID transceiver, a WiFi transceiver, a Bluetooth transceiver or a BLEtransceiver) which transmits over electromagnetic waves. In anotherembodiment, the control circuit 142 and the radio frequency transceiver144 can be implemented by one integrated circuit unit, such as a radiofrequency transceiver with a control logic component. The radiofrequency transceiver 144 is able to receive the radio frequency packetRP from the radio frequency transceiver 124. The ultrasound transceiver146 can also be a wireless communication transceiver which transmitsover ultrasound waves. The ultrasound transceiver 146 is able to receivethe ultrasound packet UP from the ultrasound transceiver 126.

In order to make sure the communication between two apparatus isperformed correctly, the first electronic apparatus 120 and the secondelectronic apparatus 140 require a common time reference or synchronizedclock signals. Details about how to do time synchronization on the firstelectronic apparatus 120 and the second electronic apparatus 140 areexplained in the following paragraphs. Reference is further made to FIG.2A, which is a flow chart illustrating a synchronization method 200according to an embodiment of the disclosure. The synchronization method200 can be utilized on the communication system 100 shown in FIG. 1.

As shown in FIG. 1 and FIG. 2A, in step S210 of the synchronizationmethod 200, the radio frequency transceiver 124 is configured togenerate a first interrupt signal to the control circuit 122. In stepS220, the radio frequency transceiver 124 is configured to transmit theradio frequency packet RP to the second electronic apparatus 140. Instep S230, the radio frequency transceiver 144 is configured to receivethe radio frequency packet RP from the first electronic apparatus 120.In step S240, the radio frequency transceiver 144 is configured togenerate a second interrupt signal to the control circuit 142 inresponse to that the radio frequency packet RP is received.

Reference is further made to FIG. 3A. FIG. 3A is a time diagramillustrating the radio frequency packet RP transmitted between the radiofrequency transceiver 124 and the radio frequency transceiver 144according to an embodiment. As shown in FIG. 3A, the radio frequencytransceiver 124 are configured to transmit the radio frequency packet RPperiodically. In the embodiment shown in FIG. 3A, there are threeconsequent frames F1, F2 and F3. In an embodiment, each of the framesF1, F2 and F3 has an equal duration length. For example, the durationsof the frames F1, F2 and F3 are all equal to a fixed radio frequencytransmission interval (e.g., 5 milliseconds or 10 milliseconds). In thiscase, the radio frequency transceiver 144 will receive one radiofrequency packet RP from the radio frequency transceiver 124 in everyone radio frequency transmission interval.

Reference is further made to FIG. 3B. FIG. 3B is a time diagramillustrating more details about the first interrupt signal INT1, theradio frequency packet RP, the second interrupt signal INT2 during theframe F1 shown in FIG. 3A according to an embodiment.

As the embodiment shown in FIG. 3B, the radio frequency transceiver 124generates the first interrupt signal INT1 to the control circuit 122(i.e., the step S210) and starts to transmit the radio frequency packetRP (i.e., the step S220) simultaneously at a time point T1.

In step S210, the first interrupt signal INT1 is configured to trigger afirst timer TC1 of the control circuit 122. In an embodiment, the firsttimer TC1 can be a time counter or a clock signal generator implementedby software/firmware programs run on the control circuit 122. In anotherembodiment, the first timer TC1 can be a frequency controlled oscillatoror a clock generating circuit implemented by hardware circuits in thecontrol circuit 122. The first interrupt signal INT1 is utilized to seta start point of the first timer TC1. As shown in FIG. 3B, the firstinterrupt signal INT1 arrive the control circuit 122 at a time point T3later than the time point T1. The first timer TC1 starts to accumulate atime count (01, 02, 03, 04, 05 . . . ) periodically from the time pointT3. In another embodiment, the first timer TC1 is implemented as a timestamp recorded at the time point T3. For example, the time stamp can be“2018-01-26-1136-36443” decided by a system clock. However, the timestamp is not limited to aforesaid format. In another embodiment, thetime stamp can include more or fewer digits according to practicalpurposes.

There is a time gap G1 between the time points T1 and T3. The time gapG1 is induced by a circuitry path between the radio frequencytransceiver 124 and the control circuit 122. In practices, the circuitrypath is usually short because the radio frequency transceiver 124 andthe control circuit 122 are both implemented in the first electronicapparatus 120. Therefore, the time gap G1 is usually shorter than 1microsecond. The first timer TC1 activates to generate a clock signalstarted from the time point T3 in response to the first interrupt signalINT1.

In step S220, as shown in FIG. 3B, the radio frequency transceiver 124starts to transmit the radio frequency packet RP at the time point T1.In an embodiment, the radio frequency transceiver 124 needs a littletime to launch and prepare the radio frequency packet RP to betransmitted. As shown in FIG. 3B, the radio frequency transceiver 124launches and prepares the radio frequency packet RP from the time pointT1 to another time point T2. The radio frequency packet RP is sent bythe radio frequency transceiver 124 from the time point T2 to anothertime point T4. A time gap G2 between the time points T1 and T4 is aprocessing time that the radio frequency transceiver 124 transmits theradio frequency packet RP.

On the other hand, in step S230, the radio frequency transceiver 144starts to receive the radio frequency packet RP from the time point T2,and the radio frequency transceiver 144 may receive the radio frequencypacket RP at the time point T4. Afterward, form the time point T4 to thetime point T5, the radio frequency transceiver 144 may confirm contentor integrity of the radio frequency packet RP. In this embodiment, theradio frequency transceiver 144 completes a receiving process of theradio frequency packet RP at the time point T5. As the embodiment shownin FIG. 3B, when the radio frequency packet is completely received atthe time point T5, the radio frequency transceiver 144 generates thesecond interrupt signal INT2 immediately to the control circuit 142 instep S240.

As shown in FIG. 1 and FIG. 3B, the second interrupt signal INT2 isconfigured to trigger a second timer TC2 of the control circuit 142. Inan embodiment, the second timer TC2 can be a time counter or a clocksignal generator implemented by software/firmware programs run on thecontrol circuit 142. In another embodiment, the second timer TC2 can bea frequency controlled oscillator or a clock generating circuitimplemented by hardware circuits in the control circuit 142.

As shown in FIG. 3B, the second interrupt signal INT2 arrive the controlcircuit 142 at a time point T6 later than the time point T5. There is atime gap G4 between the time points T5 and T6. The time gap G4 isinduced by a circuitry path between the radio frequency transceiver 144and the control circuit 142. In practices, the circuitry path is usuallyshort because the radio frequency transceiver 144 and the controlcircuit 142 are both implemented in the second electronic apparatus 140.Therefore, the time gap G4 is usually shorter than 1 microsecond. Thesecond timer TC2 is activated to accumulate a time count after the timepoint T6 in response to the second interrupt signal INT2.

In order to achieve time synchronization on the first electronicapparatus 120 and the second electronic apparatus 140, the time count onthe second timer TC2 is desired to be in the same as the time count onthe first timer TC1. To achieve aforesaid purpose, the control circuit142 is required to examine an predict time (i.e., the time point T3)when the first timer TC1 activates to accumulate the time count, suchthat the control circuit 142 can match the time count on the secondtimer TC2 to be in the same as the time count on the first timer TC1.

As shown in FIG. 3B, there is a time gap G5 between the time point T6and the time point T3. If the second electronic apparatus 140 can obtaina length of the time gap G5, the control circuit 142 can calculate thetime point T3 by “T3=T6−G5”.

As shown in FIG. 3B, a total length of the time gaps G1 and G5 is equalto a total length of the time gaps GRP and G4. Aforesaid relationshipcan be represented as:

G1+G5=GRP+G4

In the embodiment, the time gap G4 of transmitting the second interruptsignal INT2 has approximate the same length as the time gap G1 oftransmitting the first interrupt signal INT1. It can be assumed thatG1=G4, such that the time gap G5 is equal to a transmission time gapGRP. The transmission time gap GRP is a total transmission time of theradio frequency packet RP started from the time point T1 to the timepoint T5. In the embodiment, the second electronic apparatus 140 doesnot know the time point T1. In the embodiment, the second electronicapparatus 140 is configured to estimate the transmission time gap GRPaccording to a length of the radio frequency packet RP.

Reference is further made to FIG. 2B, which is a flow chart illustratingfurther steps S241-S243 in the step S240 in FIG. 2A. As shown in FIG.2B, in step S241, the second electronic apparatus 140 recognize thelength of the radio frequency packet RP. In an embodiment, the length ofthe radio frequency packet RP can be recognized by the second radiofrequency transceiver 144. The second radio frequency transceiver 144can calculate the length of the radio frequency packet RP. In anotherembodiment, the length of the radio frequency packet RP is predeterminedand known by the first electronic apparatus 120 and the secondelectronic apparatus 140.

For example, the length of the radio frequency packet RP is 32 bytes, 64bytes or 128 bytes. The time gap G3 can be determined by the length ofthe radio frequency packet RP. For example, the time gap G3 can be 360microseconds when the length of the radio frequency packet RP is 32bytes; and the time gap G3 can be 720 microseconds when the length ofthe radio frequency packet RP is 64 bytes. The transmission time gap GRPis slightly longer than the time gap G3. In step S242, the secondelectronic apparatus 140 estimates the transmission time gap GRP fromthe first radio frequency transceiver 124 starting to transmit the radiofrequency packet RP (at the time point T1) until the second radiofrequency transceiver 144 completely receiving the radio frequencypacket RP (at the time point T5) according the length of the radiofrequency packet.

For example, if the length of the radio frequency packet is 32 bytes,the second electronic apparatus 140 estimates the transmission time gapGRP to be 361 microseconds (=G3+1 microsecond). If the length of theradio frequency packet is 64 bytes, the second electronic apparatus 140estimates the transmission time gap GRP to be 721 microseconds (=G3+1microsecond). The difference of aforesaid 1 microsecond is induced bythe radio frequency transceiver 124 in preparation of the radiofrequency packet RP. In this case, the second electronic apparatus 140is able to calculate the predicted time of the time point T3 as“T3=T6−GRP”. In step S243, the second radio frequency transceiver 144generates the second interrupt signal INT2 for synchronizing the secondtimer TC2 to a time count determined by an arrival time (i.e., the timepoint T6) of the second interrupt signal INT2 and the transmission timegap GRP.

As shown in FIG. 3B, the time count on the second timer TC2 is in thesame number as the clock signal on the first timer TC1 (which started asthe time point T3). In an embodiment, the second electronic apparatus140 estimates the transmission time gap GRP and/or the predicted time ofthe time point T3, and accordingly the second electronic apparatus 140controls the second timer TC2 to start counting from the time count“12”, such that the time count on the second timer TC2 is in the sametime count as the time count on the first timer TC1.

In another embodiment, the second electronic apparatus 140 is able toestimate the time stamp of the first timer TC1 according to thetransmission time gap GRP and the arrival time (i.e., the time point T6)of the second interrupt signal INT2. For example, a time stampcorresponding to the time point T6 is examined by the control circuit142 to be “2018-01-26-1136-36454” and the transmission time gap GRP isestimated by the control circuit 142 to be 11 millisecond, such that thetime stamp on the first timer TC1 can be predicted by the controlcircuit 142 to be “2018-01-26-1136-36443”.

In this case, even the first timer TC1 and the second timer TC2 arestarted after different time points, the time counts on the first timerTC1 and the second timer TC2 can be the identical. The second electronicapparatus 140 can modulate the time count on the second timer TC2according to the transmission time gap GRP of the radio frequency packetRP. As shown in FIG. 2A, the synchronization method 200 is able tosynchronize the first timer TC1 and the second timer TC2 on twoelectronic apparatus 120 and 140 through steps S210-S240.

In an embodiment, the first electronic apparatus 120 is a controllerdevice of a virtual reality system, and the second electronic apparatus140 is a head-mounted display device of the virtual reality system. Inthis case, the controller device and the head-mounted display device ofthe virtual reality system can communicate with each other insynchronized time reference based on the synchronization method 200shown in aforesaid embodiments. The disclosure is not limited thereto.In another embodiment, the first electronic apparatus 120 is thehead-mounted display device of the virtual reality system, and thesecond electronic apparatus 140 is the controller device of the virtualreality system.

In an embodiment, the second radio frequency transceiver 144 furthertransmits an acknowledge packet ACK to the first radio frequencytransceiver 124 after the radio frequency packet RP is received.Reference is further made to FIG. 4A and FIG. 4B. FIG. 4A is a timediagram illustrating the radio frequency packet RP and the acknowledgepacket ACK transmitted between the radio frequency transceiver 124 andthe radio frequency transceiver 144 according to an embodiment.

In the embodiment shown in FIG. 4A, there are three consequent framesF1, F2 and F3. In an embodiment, each of the frames F1, F2 and F3 has anequal duration length. For example, the durations of the frames F1, F2and F3 are all equal to a fixed radio frequency transmission interval(e.g., 5 milliseconds or 10 milliseconds). In this case, the radiofrequency transceiver 144 will receive one radio frequency packet RPfrom the radio frequency transceiver 124 in every one radio frequencytransmission interval. After receiving the radio frequency packet RP,the radio frequency transceiver 144 will send the acknowledge packet ACKback to the radio frequency transceiver 124. The radio frequencytransceiver 124 will receive the acknowledge packet ACK from the radiofrequency transceiver 144.

FIG. 4B is a time diagram illustrating more details about the firstinterrupt signal INT1, the radio frequency packet RP, the secondinterrupt signal INT2 and a ultrasound signal US during the frame F1shown in FIG. 4A according to an embodiment. The relationships anddetails about the first interrupt signal INT1, the radio frequencypacket RP, the second interrupt signal INT2 in FIG. 4B are similar toaforesaid embodiment shown in FIG. 3B, and not to be repeated here.

In an embodiment, the communication system 100 can perform further stepsS250-S280 to transmit an ultrasound packet UP based on the synchronizedtime counts on the first timer TC1 and the second timer TC2. As shown inFIG. 1 and FIG. 4B, in step S250, when the first timer TC1 startscounting (at the time point T3 in FIG. 4B) after being triggered by thefirst interrupt signal INT1, the first ultrasound transceiver 126 sendsan ultrasound signal US1 as shown in FIG. 4B. The ultrasound packet UPis sent over the ultrasound signal US1 at the time point T3 inaccordance with the first timer TC1. In this embodiment, a transmissionof the ultrasound packet from the first ultrasound transceiver 126starts at the time point T3. The second ultrasound transceiver 146receives an ultrasound signal US2 as shown in FIG. 4B. The ultrasoundpacket UP is received in the ultrasound signal US2 by the secondultrasound transceiver 146 at the time point T7.

In step S260, the first ultrasound transceiver 126 transmits theultrasound packet UP in an ultrasound active time slot UATS as shown inFIG. 4B. In step S270, the second ultrasound transceiver 146 receivesthe ultrasound packet UP. In step S280, the second ultrasoundtransceiver 146 samples the ultrasound packet UP in accordance with thesecond timer TC2. For example, the data in the ultrasound packet UP isprocessed, decoded or decrypted with the clock signal on the secondtimer TC2. Because the second timer TC2 is synchronized with the firsttimer TC1, a travelling time UTT of the ultrasound packet UP from theultrasound transceiver 126 to the ultrasound transceiver 146 can becalculated in reference to the second timer TC2. In this case, when theultrasound packet UP is received by the ultrasound transceiver 146 cansend another interrupt signal to the control circuit 142. The controlcircuit 142 will notice that the ultrasound packet UP is received at thetime point T7, which correspond to the time count “18” on the secondtimer TC2. The control circuit 142 can calculate the travelling time UTTby “UTT=T7−T3”. In the embodiment shown in FIG. 4B, the travelling timeUTT is equal to 17 units (=18-01) of time counts on the second timer TC2(or the first timer TC1).

In an embodiment, the first timer TC1 and the second timer TC2 may stillhave slight timing difference, which is also known as a timing jitter.In one embodiment, the timing jitter between first timer TC1 and thesecond timer TC2 should be less than 3 milliseconds, such that the firstelectronic apparatus 120 and the second electronic apparatus 140 can besynchronized with accuracy at a millisecond-scaler level.

As shown in FIG. 4B, the radio frequency transceiver 144 will send theacknowledge packet ACK back to the radio frequency transceiver 124 afterthe time point T5. Afterward, the radio frequency transceiver 124 willreceive the acknowledge packet ACK from the radio frequency transceiver144. As shown in FIG. 4B, the ultrasound signal US1 is utilized totransmit an ultrasound packet in the ultrasound active time slot UATS.

In an embodiment, the acknowledge packet ACK is utilized to carry anadjustment command from the second electronic apparatus 140 to the firstelectronic apparatus 120. The first electronic apparatus 120 adjusts theultrasound active time slot UATS according to the adjustment command inthe acknowledge packet ACK. For example, the ultrasound active time slotUATS can be widen, shorten, shifted to be earlier or later according tothe adjustment command carried in the acknowledge packet ACK.

In aforesaid embodiment shown in FIG. 2 and FIG. 4B, the synchronizationbetween the first timer TC1 and the second timer TC2 is utilized todetermine the travelling time UTT of the ultrasound packet UP betweenthe first electronic apparatus 120 and the second electronic apparatus140, such that the second electronic apparatus 140 can measure arelative distance to the first electronic apparatus 120 according to thetravelling time UTT. The disclosure is not limited thereto. In otherembodiments, the synchronization between the first timer TC1 and thesecond timer TC2 can be utilized to synchronize SimultaneousLocalization and Mapping (SLAM) data, camera explore behaviors, videoframes and/or inertial Measurement Unit (IMU) data timestamps ondifferent electronic apparatus.

Aforesaid embodiments illustrate that there are two electronic apparatus120 and 140 in the communication system 100, and the disclosure is notlimited to two electronic apparatus. Reference is further made to FIG.5, which is a functional block diagram illustrating a communicationsystem 300 according to an embodiment of the disclosure.

In the embodiment shown in FIG. 5, the communication system 300 includesa first electronic apparatus 320, a second electronic apparatus 340 anda third electronic apparatus 360.

The first electronic apparatus 320 and the second electronic apparatus340 are able to communicate with each other. For example, data,commands, and/or control signals can be transmitted from the firstelectronic apparatus 320 to the second electronic apparatus 340 or fromthe second electronic apparatus 340 to the first electronic apparatus320. The third electronic apparatus 360 and the second electronicapparatus 340 are able to communicate with each other. For example,data, commands, and/or control signals can be transmitted from the thirdelectronic apparatus 360 to the second electronic apparatus 340 or fromthe second electronic apparatus 340 to the third electronic apparatus360.

As shown in FIG. 5, the first electronic apparatus 320 includes acontrol circuit 322, a radio frequency transceiver 324 and an ultrasoundtransceiver 326. The second electronic apparatus 340 include a controlcircuit 342, a radio frequency transceiver 344 a, another radiofrequency transceiver 344 b and an ultrasound transceiver 346. The thirdelectronic apparatus 360 include a control circuit 362, a radiofrequency transceiver 364 and an ultrasound transceiver 366.

The radio frequency transceiver 324 of the first electronic apparatus320 is configured to transmit a radio frequency packet RP1 to the radiofrequency transceiver 344 a of the second electronic apparatus 340, andsimultaneously generates an interrupt signal to trigger a timer TC1 inthe control circuit 322. The radio frequency transceiver 364 of thethird electronic apparatus 360 is configured to transmit another radiofrequency packet RP2 to the radio frequency transceiver 344 b of thesecond electronic apparatus 340, and simultaneously generate aninterrupt signal to trigger the timer TC3 in the control circuit 362.The radio frequency transceiver 344 a generate an interrupt signal totrigger a timer TC2 a in the second control circuit 342 in response tothat the radio frequency packet RP1 is received. The radio frequencytransceiver 344 b generate an interrupt signal to trigger a timer TC2 bin the second control circuit 342 in response to that the radiofrequency packet RP2 is received.

The ultrasound transceiver 326 of the first electronic apparatus 320 isconfigured to transmit an ultrasound packet UP1 to the radio ultrasound346 of the second electronic apparatus 340. The ultrasound transceiver366 of the third electronic apparatus 360 is configured to transmitanother ultrasound packet UP2 to the ultrasound transceiver 346 of thesecond electronic apparatus 340.

The first electronic apparatus 320 and the second electronic apparatus340 are able to utilize the synchronization method 200 in aforesaidembodiments to synchronize the timer TC1 and the timer TC2 a. Detailsabout how to synchronize are disclosed in aforesaid embodiments and notto be repeated here. Similarly, the third electronic apparatus 360 andthe second electronic apparatus 340 are able to utilize thesynchronization method 200 in aforesaid embodiments to synchronize thetimer TC3 and the timer TC2 b. Therefore, the ultrasound packet UP1 andthe ultrasound packet UP2 can be processed with synchronized clocksignals.

In addition, the radio frequency transceiver 344 a of the secondelectronic apparatus 340 is able to transmit an acknowledge packet ACK1to the first electronic apparatus 320, and the radio frequencytransceiver 344 b of the second electronic apparatus 340 is able totransmit another acknowledge packet ACK2 to the third electronicapparatus 360. The acknowledge packets ACK1 and ACK2 are able to carryadjustment commands from the second electronic apparatus 340 to thefirst electronic apparatus 320 and the third electronic apparatus 360.The adjustment commands are configured to differentiate the ultrasoundactive time slots utilized by the first electronic apparatus 320 and thethird electronic apparatus 360. In an embodiment, the adjustmentcommands are configured to separate the ultrasound active time slotsinto two non-overlapping periods. In this case, the ultrasound activetime slot utilized by the first electronic apparatus 320 is differentfrom and not overlapped with the ultrasound active time slot utilized bythe third electronic apparatus 360. The ultrasound packet UP1 and theultrasound packet UP2 will not be interfere with each other, and thesecond electronic apparatus 340 can easily recognize an origin of theultrasound packet UP1 or the ultrasound packet UP2 according theultrasound active time slots.

In an embodiment, the first electronic apparatus 320 and the thirdelectronic apparatus 360 are controller devices of a virtual realitysystem, and the second electronic apparatus 340 is a head-mounteddisplay device of the virtual reality system. In this case, thecontroller device and the head-mounted display device of the virtualreality system can communicate with each other in synchronized timereference based on the synchronization method 200 shown in aforesaidembodiments.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A communication system, comprising: a firstelectronic apparatus, comprising: a first control circuit; a first radiofrequency transceiver coupled with the first control circuit, the firstradio frequency transceiver being configured to generate a firstinterrupt signal to the first control circuit and transmit a radiofrequency packet; and a first wireless communication transceiverconfigured to transmit an wireless communication packet in an wirelesscommunication active time slot; and a second electronic apparatus,comprising: a second control circuit; a second radio frequencytransceiver coupled with the second control circuit, the second radiofrequency transceiver being configured to receive the radio frequencypacket and generate a second interrupt signal to the second controlcircuit in response to that the radio frequency packet is received; anda second wireless communication transceiver configured to receive thewireless communication packet from the first electronic apparatus;wherein the first interrupt signal is configured to trigger a firsttimer of the first control circuit, the second interrupt signal isconfigured to trigger a second timer of the second control circuit, thesecond timer is synchronized with the first timer or a timestamp of thefirst timer is estimated according to the second interrupt signal andthe radio frequency packet, wherein a first transmission latency betweenthe first radio frequency transceiver and the second radio frequencytransceiver is shorter than a second transmission latency between thefirst wireless communication transceiver and the second wirelesscommunication transceiver, wherein the wireless communication packet isgenerated by the first wireless communication transceiver in accordancewith the first timer, and the wireless communication packet is sampledby the second wireless communication transceiver in accordance with thesecond timer.
 2. The communication system of claim 1, wherein the firstradio frequency transceiver generates the first interrupt signal andstarts to transmit the radio frequency packet simultaneously, and thesecond radio frequency transceiver generates the second interrupt signalimmediately when the radio frequency packet is completely received. 3.The communication system of claim 1, wherein a length of the radiofrequency packet transmitted from the first electronic apparatus isrecognized by the second electronic apparatus, the second electronicapparatus estimates a transmission time gap from the first radiofrequency transceiver starting to transmit the radio frequency packetuntil the second radio frequency transceiver completely receiving theradio frequency packet according to the length of the radio frequencypacket.
 4. The communication system of claim 3, wherein the second timeris activated by the second interrupt signal and the second timer issynchronized to a time count determined by an arrival time of the secondinterrupt signal received by the second control circuit and thetransmission time gap.
 5. The communication system of claim 1, whereinthe second radio frequency transceiver is configured to transmit anacknowledge packet to the first radio frequency transceiver after theradio frequency packet is received.
 6. The communication system of claim5, wherein the acknowledge packet carries an adjustment command from thesecond electronic apparatus to the first electronic apparatus, the firstelectronic apparatus adjust the wireless communication active time slotaccording to the adjustment command.
 7. The communication system ofclaim 1, wherein the first electronic apparatus is a controller deviceor a head-mounted display device of a virtual reality system, and thesecond electronic apparatus is the controller device or the head-mounteddisplay device of the virtual reality system.
 8. A synchronizationmethod, suitable between a first electronic apparatus and a secondelectronic apparatus, the synchronization method comprising: generating,by a first radio frequency transceiver, a first interrupt signal totrigger a first timer on the first electronic apparatus; transmitting aradio frequency packet from the first electronic apparatus to the secondelectronic apparatus; in response to that the radio frequency packet isreceived by the second electronic apparatus, generating, by a secondradio frequency transceiver, a second interrupt signal to trigger asecond timer on the second electronic apparatus, wherein the secondtimer is synchronized with the first timer or a timestamp of the firsttimer is estimated according to the second interrupt signal and theradio frequency packet; and transmitting an wireless communicationpacket in an wireless communication active time slot from the firstelectronic apparatus to the second electronic apparatus, wherein a firsttransmission latency between the first radio frequency transceiver andthe second radio frequency transceiver is shorter than a secondtransmission latency between a first wireless communication transceiverand a second wireless communication transceiver, wherein the wirelesscommunication packet is generated by the first wireless communicationtransceiver in accordance with the first timer, and the wirelesscommunication packet is sampled by the second wireless communicationtransceiver in accordance with the second timer.
 9. The synchronizationmethod of claim 8, wherein the first interrupt signal is generatedsimultaneously with the first electronic apparatus and starts totransmit the radio frequency packet, and the second interrupt signal isgenerated immediately when the radio frequency packet is completelyreceived by the second electronic apparatus.
 10. The synchronizationmethod of claim 8, further comprising: recognizing, by the secondelectronic apparatus, a length of the radio frequency packet transmittedfrom the first electronic apparatus; and estimating, by the secondelectronic apparatus, a transmission time gap from the first radiofrequency transceiver starting to transmit the radio frequency packetuntil the second radio frequency transceiver completely receiving theradio frequency packet according to the length of the radio frequencypacket.
 11. The synchronization method of claim 10, wherein the secondtimer is activated by the second interrupt signal and the second timeris synchronized to a time count determined by an arrival time of thesecond interrupt signal and the transmission time gap.
 12. Thesynchronization method of claim 8, wherein the wireless communicationpacket is generated by the first electronic apparatus in accordance withthe first timer, and the wireless communication packet is sampled by thesecond electronic apparatus in accordance with the second timer.
 13. Thesynchronization method of claim 12, further comprising: transmitting anacknowledge packet from the second electronic apparatus to the firstelectronic apparatus after the radio frequency packet is received. 14.The synchronization method of claim 13, wherein the acknowledge packetcarries an adjustment command from the second electronic apparatus tothe first electronic apparatus, the synchronization method furthercomprising: adjusting, by the first electronic apparatus, the wirelesscommunication active time slot according to the adjustment command.